Repeated Multiple Maternities in Triplet Families

Abstract

In earlier studies, scientists have attempted to identify genetic and environmental factors affecting the rate of multiple maternities among humans. We contribute to these studies by analysing the frequencies of multiple maternities in sibships containing triplets. Use of the Hellin transformation is included in evaluation of the triplet rate. Our results indicate greater frequencies of repeated multiple maternities in the sibships than expected, based on population frequencies. The excesses obtained are more marked in triplet maternities than in twin maternities. The transformed triplet rate shows results similar to the twinning rate. The findings also indicate that in families, the influence of maternal factors on the frequencies of multiple maternities is stronger than the influence of paternal factors.Key words: Hellin's law, maximum likelihood, probability models, parameter transformationsStudies have been performed to identify genetic and environmental factors affecting the rate of multiple maternities among humans (e.g., Bulmer, 1970;Weinberg, 1902). Fellman and Eriksson (1990) developed models previously presented by Hellin (1895), Peller (1946), andEriksson et al. (1973). They presented the probability model:where P st is the probability that a sibship contains s twin pairs and t triplet sets, w is the probability of a twin set and r is the probability of a triplet set. However, they had no information about sibships without twin pairs and triplet sets. Fellman and Eriksson (1990) stressed that a sibship could be included in their study only if it contained multiple maternities. Consequently, their data sets resulted in the distribution being truncated and they had to cope with the conditional probabilityThis truncation complicated the parameter estimation. They needed to apply iterative numerical processes in order to obtain maximum likelihood estimates .In this study, we modify the Fellman-Eriksson model so that it can be applied to sibships that contain triplet sets. Material and Methods MaterialOur data consist of sibships containing triplets initially presented by Miettinen (1954). We have studied these data in different contexts (Eriksson & Fellman, 1986;Eriksson et al., 1990Eriksson et al., , 2007Fellman & Eriksson, 2014). The family data set comprises triplets born in Finland from 1905 to 1959. During this period, 723 triplet sets were registered in the official Finnish birth records. Using genealogical studies, sibships of the triplets and of their parents were collected. The genealogical investigations, initiated by Miettinen (1954) and continued by our group, resulted in birth information for 642 sibships of triplets containing 650 triplet sets and 125 twin pairs. Consequently, almost 90% of all officially registered triplet sets were included in our family series. Our data are presented in Table 1.For sake of comparison, we include in this study the distributions of multiple maternities in sibships of the triplet mothers and triplet fathers. There are 587 sibships of mothers containing 3 tri...

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

“…would not seem to be responsible for this secondary split. It has been suggested that this type of MZ twinning could be related to a uterine, endometrial, or early pregnancy factor somehow playing a role in increasing the likelihood for this secondary MZ twin split to occur around the time of implantation (Aston et al, 2008; Burton et al, 2007; Choux et al, 2015; Fellman & Eriksson, 2014; Fennessy et al, 2015; Gray et al, 2001; Guilherme et al, 2008; James et al, 2012; Klein et al, 2006; Sklar et al, 2017; Yovich et al, 1984). In addition, when two ova “appear” in the uterus, one may already be “overripe,” therefore being at risk for ova splitting.…”